Brake control

ABSTRACT

An apparatus including a controller configured to generate a first indication for a vehicle braking system depending upon an oxidation state of a wheel brake of the vehicle is disclosed. Also disclosed is a braking system including a controller configured to receive a first indication, the first indication having been generated depending upon an oxidation state of a wheel brake of a vehicle and control the operation of the brake based on the first indication. Also disclosed is a method of controlling at least one brake of an aircraft, and an aircraft including the apparatus, the braking system and a temperature sensor configured to measure a temperature of a wheel brake of the aircraft and to transmit the temperature measurement to the apparatus.

CROSS RELATED APPLICATIONS

This application claims priority to United Kingdom (GB) PatentApplication 1803203.7, filed Feb. 27, 2018, and United Kingdom (GB)Patent Application 1811178.1, filed Jul. 6, 2018, the entire contents ofeach of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to brake control and particularly,although not exclusively, to brake control taking account of a state,such as an oxidation state, of the brake.

BACKGROUND

Vehicle brakes may include components such as brake discs composed ofCarbon-Carbon composites. The brakes may undergo thermal oxidation athigh temperatures as carbon atoms in the brake discs react with oxygen.The brakes may need to be serviced or replaced once a certain amount ofthermal oxidation has taken place for safe functioning of the vehicle

SUMMARY

A first aspect of the present invention provides an apparatuscomprising: a controller configured to: generate a first indication fora vehicle braking system depending upon an oxidation state of a wheelbrake of the vehicle.

Optionally, the controller is configured to determine a braketemperature characteristic criterion of the brake according to theoxidation state of the brake; determine whether a temperaturecharacteristic of the brake satisfies the brake temperaturecharacteristic criterion; and generate the first indication for thebraking system depending upon whether the brake temperaturecharacteristic satisfies the brake temperature characteristic criterion.

Optionally, the controller receives an indication of the temperaturecharacteristic of the brake from a temperature sensor associated withthe brake.

Optionally, the controller receives a predicted temperaturecharacteristic from a brake temperature prediction function as thetemperature characteristic of the brake.

Optionally, the controller is configured to: monitor the temperaturecharacteristic of the brake; and if the temperature characteristic ofthe brake no longer satisfies the brake temperature characteristiccriterion, generate a second indication for the braking system that thetemperature characteristic of the brake no longer satisfies the braketemperature characteristic criterion.

Optionally, the temperature characteristic of the brake comprises atemperature of the brake; and the brake temperature characteristiccriterion is satisfied if the temperature of the brake exceeds a braketemperature threshold.

Optionally, the controller is configured such that the higher the levelof thermal oxidation of the brake, the lower the brake temperaturethreshold of the determined brake temperature characteristic criterionis.

Optionally, if the thermal oxidation state of the brake is below apredetermined thermal oxidation level, a first brake temperaturecharacteristic criterion is selected which comprises a first temperaturethreshold.

Optionally, if the thermal oxidation state of the brake is above thepredetermined thermal oxidation level, a second brake temperaturecharacteristic criterion is selected which comprises a secondtemperature threshold lower than the first temperature threshold

Optionally, the second brake temperature characteristic criterion isselected based on the difference between the thermal oxidation state ofthe brake and the predetermined thermal oxidation level.

Optionally, the first temperature threshold is above 400° C.

A second aspect of the present invention provides a braking system of avehicle, the braking system comprising a controller configured to:receive a first indication, the first indication having been generateddepending upon an oxidation state of a wheel brake of a vehicle; andcontrol the operation of the brake based on the first indication.

Optionally, in the braking system according to the second aspect, thefirst indication received by the controller is generated depending uponwhether a brake temperature characteristic satisfies a brake temperaturecharacteristic criterion; and the controller is configured to: receive asecond indication that the temperature characteristic of the brake nolonger satisfies the brake temperature characteristic criterion; andcontrol the brake selectively to be enabled or disabled based on thereceived indication.

Optionally, in the braking system according to the second aspect, thecontroller is configured to control the brake to be disabled if itreceives the first indication.

Optionally, in the braking system according to the second aspect, thecontroller is configured to control the brake to be enabled if itreceives the second indication.

Optionally, in the braking system according to the second aspect, thevehicle is an aircraft and the controller is configured to disable abrake if a taxiing criterion is met, wherein the taxiing criterioncomprises one or more of: an aircraft speed threshold defined such thatan aircraft speed less than or equal to the aircraft speed thresholdsatisfies the predefined taxiing criterion; and a particular flightphase indicated by a flight phase indication system of the aircraft.

Optionally, in the braking system according to the second aspect, thecontroller is configured to: receive a braking request, the brakingrequest comprising information relating to a requested brakingintensity; determine, based on the information related to the requestedbraking intensity, whether the requested braking intensity exceeds abraking intensity threshold; and if the requested braking intensityexceeds the braking intensity threshold, enable at least one disabledbrake.

A third aspect of the present invention provides a method forcontrolling at least one brake of an aircraft, the method comprising:generating a first indication depending upon an oxidation state of awheel brake of an aircraft; and controlling the brake to be disabledbased on the first indication.

Optionally, the method according to the third aspect comprises:determining a brake temperature characteristic criterion of the brakeaccording to the thermal oxidation state of the brake; determiningwhether a temperature characteristic of the brake satisfies the braketemperature characteristic criterion; and generating the firstindication depending upon whether the brake temperature characteristicsatisfies the brake temperature characteristic criterion.

Optionally, the method according to the third aspect comprises: (i)monitoring the temperature characteristic of the brake; (ii) determiningwhether the temperature characteristic of the brake still satisfies thebrake temperature characteristic criterion; if the temperaturecharacteristic of the brake no longer satisfies the brake temperaturecharacteristic criterion: generating a second indication that thetemperature characteristic of the brake no longer satisfies the braketemperature characteristic criterion; and controlling the brake to beenabled based on the second indication; and if the temperaturecharacteristic of the brake still satisfies the brake temperaturecharacteristic criterion, repeating (i) and (ii).

Optionally, the method according to the third aspect comprises receivingan indication of the temperature characteristic of the brake from atemperature sensor associated with the brake.

Optionally, the method according to the third aspect comprises receivinga predicted temperature characteristic from a brake temperatureprediction function as the temperature characteristic of the brake.

Optionally, in the method according to the third aspect, the temperaturecharacteristic of the brake comprises a temperature of the brake; andthe brake temperature characteristic criterion is satisfied if thetemperature of the brake exceeds a brake temperature threshold.

Optionally, in the method according to the third aspect, the higher thelevel of thermal oxidation of the brake, the lower the brake temperaturethreshold of the determined brake temperature characteristic criterionis.

Optionally, in the method according to the third aspect, if the thermaloxidation state of the brake is below a predetermined thermal oxidationlevel, a first brake temperature characteristic criterion is selectedwhich comprises a first temperature threshold.

Optionally, in the method according to the third aspect, if the thermaloxidation state of the brake is above the predetermined thermaloxidation level, a second brake temperature characteristic criterion isselected which comprises a second temperature threshold lower than thefirst temperature threshold.

Optionally, in the method according to the third aspect, the secondbrake temperature characteristic criterion is selected based on thedifference between the thermal oxidation state of the brake and thepredetermined thermal oxidation level.

Optionally, in the method according to the third aspect, the firsttemperature threshold is above 400° C.

Optionally, in the method according to the third aspect, the brake isdisabled if a predefined taxiing criterion is met, wherein thepredefined taxiing criterion comprises one or more of: an aircraft speedthreshold defined such that an aircraft speed less than or equal to theaircraft speed threshold satisfies the predefined taxiing criterion; anda particular flight phase indicated by a flight phase indication systemof the aircraft.

Optionally, the method according to the third aspect comprises:receiving a braking request, the braking request comprising informationrelating to a requested braking intensity; determining, based on theinformation related to the requested braking intensity, whether therequested braking intensity exceeds a braking intensity threshold; andif the requested braking intensity exceeds the braking intensitythreshold, enabling at least one disabled brake.

A fourth aspect of the present invention provides an aircraftcomprising: an apparatus according to the first aspect; a braking systemaccording to the second aspect; and a temperature sensor configured tomeasure a temperature of a wheel brake of the aircraft and to transmitthe temperature measurement to the apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic view of an aircraft on which examples may bedeployed;

FIG. 2 is a schematic view of a brake and a wheel of an aircraft landinggear according to an example;

FIG. 3 is a schematic view of an apparatus and a braking system of avehicle according to an example;

FIG. 4a is a first flow diagram of a method of controlling at least onebrake of an aircraft according to an example;

FIG. 4b is a second flow diagram of a method of controlling at least onebrake of an aircraft according to an example;

FIG. 4c is a third flow diagram of a method of controlling at least onebrake of an aircraft according to an example;

FIG. 5 is a fourth flow diagram of a method of controlling at least onebrake of an aircraft according to an example;

FIG. 6 is a flow diagram of an exemplary method of determining thethermal oxidation state of a brake of an aircraft landing gear;

FIG. 7 is a flow diagram of an exemplary method of determining thethermal oxidation state of a brake of an aircraft landing gear;

FIG. 8 is an exemplary graph illustrating the temperature of a brakewith respect to time;

FIG. 9 is an exemplary graph illustrating the thermal oxidation state ofa brake with respect to time for a specific temperature;

FIG. 10 is an exemplary flow diagram of a method of determining anamount of brake wear according to an example; and

FIG. 11 is an exemplary flow diagram of a method of predicting a numberof good future use cycles with respect to an aircraft brake according toan example.

DETAILED DESCRIPTION

The following disclosure relates to systems and processes for limitinguse of a brake of a vehicle, e.g. aircraft brakes, when the brakereaches certain high temperatures, for the purposes of reducing theamount of thermal oxidation of the brake during use.

FIG. 1 is a simplified schematic view of an aircraft 100. The aircraft100 comprises a plurality of landing gear assemblies 102. The landinggear assemblies may include main and nose landing gears that may beextended during take-off and landing. Each landing gear assembly 102includes wheels such as wheel 104. The aircraft 100 comprises acomputing system 106, which may, for example, comprise one or moreprocessors and one or more computer readable storage media. The aircraft100 may also comprise instruments 108, such as instruments or sensorsfor measuring characteristics or parameters related to the aircraft, andinstruments or sensors for measuring environmental characteristics. Itshould be appreciated that, in some examples, the instruments 108 may bedistributed at various different locations of the aircraft 100.

FIG. 2 is a simplified schematic view of a brake 200 associated with thewheel 104 of the aircraft 100. Each of the wheels of the aircraft 100may have associated with it a brake such as brake 200. The brake 200applies a braking force to inhibit the rotation of the wheel 104. Inthis example, the brake 200 comprises a plurality of brake discs 202including a pressure plate 204, a reaction plate 206, and a number ofrotors and stators such as the rotor 208 and the stator 210. In thisexample, the brake discs 202 include a plurality of rotors and stators,and the brake assembly 200 is therefore a multiple disc brake. In otherexamples, the brake assembly 200 may not be a multiple-disc brake. Itwill be understood that the type of brake used in an aircraft landinggear depends on the characteristics of the aircraft in question, such assize, carrying capacity and the like.

When the aircraft 100 travels along the ground supported by the landinggear 102, the rotors rotate with the wheel 104, whereas the stators, thepressure plate 204 and the reaction plate 206 do not rotate with thewheel 104. When braking is applied, the pressure plate 204 is urgedtowards the reaction plate 206 so that the brake discs 202 come intocontact with one another (as shown in box 212 of FIG. 2) and frictionacts to inhibit the rotational motion of the rotors, thus generating abraking force.

Any one or more of the rotors, stators, pressure plate 204 and thereaction plate 206 may be composed of Carbon-Carbon (CC) composites. Abrake including brake discs composed of CC composites may be referred toas a carbon brake. For example, the brake discs 202 may be composed of agraphite matrix reinforced by carbon fibers. During use, the brake discs202 may undergo oxidation. During an oxidation reaction, oxygen reactswith the carbon of the brake discs 202 causing carbon atoms to beremoved from the brake discs 202 as carbon dioxide and/or carbonmonoxide is produced leading to a loss of mass. The oxidationstate/level of the brake 200 may be expressed as an amount of mass lostdue to oxidation.

The brake discs 202 may oxidise via catalytic oxidation or thermaloxidation. Catalytic oxidation may occur when the oxidation reaction isaided by the action of a catalyst. For example, alkali metals are knowncatalysts for oxidation of CC composites. Catalytic oxidation may berelevant in areas where the air has relatively high salinity. Catalyticoxidation may also be relevant at airports that use runway deicerscomprising alkali salts. Thermal oxidation of the brake discs 202 mayoccur if the brake discs 202 reach high temperatures. During use, thebrake 200, specifically the brake discs 202, may reach hightemperatures. This is because when the brake 200 is applied to reducethe speed of the aircraft 100, some of the kinetic energy of theaircraft 100 is absorbed into the brake assembly 200 as heat causing itstemperature to rise. In the present examples, the components of thebrake 200 composed of CC composites (i.e. the brake discs 202) undergooxidation. However, the present disclosure hereafter refers to theoxidation state of the brake 200.

The aircraft 100 may comprise a braking system 214, which controls theoperation of the brake 200. The braking system 214 causes the brake 200to be applied in response to a braking request (e.g. when a pilot of theaircraft 100 presses a brake pedal). For example, the brake 200 may behydraulically actuated or electrically actuated, and the braking system214 may control the brake actuation system (not shown) to apply thebrake 200. The braking system 214 may communicate with the brakeactuation system via a wireless or wired communication link.

FIG. 3 is a simplified schematic view of an apparatus 300 and thebraking system 214. The apparatus 300 comprises a controller 302. Thecontroller 302 is configured to generate a first indication for thebraking system 214 depending upon an oxidation state of the brake 200.For example, the apparatus 300 may be installed on a vehicle such as theaircraft 100 to generate the first indication in relation to the brake200. The apparatus 300 may be installed on any kind of vehicle whichcomprises one or more braked wheels. Nevertheless, for convenience, thefollowing description will be in the context of the aircraft 100.

In the example of FIG. 3, the braking system 214 comprises a controller304. Hereafter, the controller 302 of the apparatus 300 is referred toas the first controller 302 and the controller 304 of the braking system214 is referred to as the second controller 304, for clarity. The secondcontroller 304 is configured to receive the first indication, the firstindication having been generated depending upon the oxidation state ofthe brake 200 (as described), and control the operation of the brake 200based on the first indication. The second controller 304 may receive anindication from the first controller 302 via a wired or wirelesscommunication link. Alternatively, the first controller 302 may writeinformation relating to the indication to a computer readable storagemedium (not shown) and the second controller 304 may read theinformation relating to the indication from said computer readablestorage medium.

The second controller 304 may be configured to control the brake 200 tobe disabled if it receives the first indication. For example, if thebrake 200 is disabled, the second controller 304 may assign a “disabled”status to it. That the brake 200 is disabled means that when the brakingsystem 214 receives a braking request, the braking system 214 does notcause the brake 200 to be applied. The required braking may instead beprovided by other brakes associated with the other wheels of the landinggear 102.

The operation of the first controller 302 and the second controller 304is illustrated by the flow diagram of FIG. 4a , which represents anexample method 400 for controlling at least one brake of the aircraft100. The method 400 may be implemented by the first and secondcontrollers 302, 304. In some examples, the process blocks of the method400 may be provided as processor-executable instructions (e.g.executable by respective processors of the first and second controllers302, 304).

At block 402, the first indication is generated depending upon theoxidation state of the brake 200. The first controller 302 of theapparatus 300 performs block 402. At block 402, the first controller 302receives information regarding the oxidation state of the brake 200 (thesource of the information is described in further detail hereafter), forexample. The first controller 302 may compare the oxidation state to aparticular threshold or may determine a criterion based on the oxidationstate and compare certain characteristics of the brake 200 to thatcriterion. Such comparisons are described in further detail hereafter.The first controller 302 may generate the first indication based on sucha comparison. If the first indication is generated, the method 400proceeds to block 404

At block 404, the brake 200 is controlled to be disabled based on thefirst indication.

In some examples, the oxidation state of the brake 200 may take intoaccount thermal oxidation (i.e. the oxidation state may be the thermaloxidation state) or catalytic oxidation (i.e. the oxidation state may bethe catalytic oxidation state). In some examples, the oxidation statemay take into account both thermal oxidation and catalytic oxidation. Inthe following examples, the oxidation state of the brake 200 takesaccount of thermal oxidation only.

In some examples, the thermal oxidation state of the brake 200 may bedetermined using the methods and systems described in an earlierunpublished application, namely GB patent application number 1803203.7,attached hereto as an Annex. For example, the thermal oxidation state ofthe brake 200 after a braking event/braking operation may be determinedusing a thermal oxidation model based on an initial thermal oxidationstate of the brake 200 before the braking event and a temperatureprofile of the brake 200 with respect to time. The first controller 302may receive the thermal oxidation state of the brake 200 from theapparatus which determines the thermal oxidation state of the brake 200.Alternatively, the up-to-date thermal oxidation state of the brake 200may be stored in a computer readable storage medium (e.g. a computerreadable storage medium which is part of the computing system 106), andthe first controller 302 may retrieve the thermal oxidation state of thebrake 200 from said computer readable storage medium. The firstcontroller 302 may retrieve the thermal oxidation state of the brake 200each time the thermal oxidation state is updated. In some examples, thefirst controller 302 may determine the thermal oxidation state of thebrake 200 as described in the earlier unpublished application.

As described, the oxidation state may be expressed as an amount of masslost due to oxidation. In some examples, the first controller 302 maycompare the oxidation state of the brake 200 to an oxidation thresholdand may generate the first indication if the oxidation threshold isreached. For example, the oxidation threshold may be between 4% and6.5%, for instance 5.7%, of the original mass of the brake 200 lost dueto oxidation. In the example where the oxidation threshold is 5.7%, theoxidation criterion may be satisfied if the thermal oxidation statereaches (i.e. is equal to or above) 5.7% of the original mass of thebrake 200 lost. In such examples, the brake 200 may be disabled if it isoxidised beyond a certain level. The oxidation threshold may be set at alevel at which service or replacement of the whole or part of the brake200 is deemed necessary for safe functioning.

Alternatively, or in addition, the first controller 302 may determine abrake temperature characteristic criterion of the brake 200 according tothe oxidation state of the brake 200. The first controller 302 maydetermine whether a temperature characteristic of the brake 200satisfies the brake temperature characteristic criterion and generatethe first indication for the braking system 214 depending upon whetherthe brake temperature characteristic satisfies the brake temperaturecharacteristic criterion. In the examples where the oxidation thresholdis also used and reached by the oxidation state of the brake 200, thefirst controller 302 may not compare the temperature characteristic tothe temperature characteristic criterion. This is because, in suchexamples, the brake 200 may simply be disabled because it is toooxidised irrespective of the temperature characteristic of the brake200. The examples described hereafter are in the context of the firstcontroller 302 comparing the temperature characteristic to thetemperature characteristic criterion.

FIG. 4b illustrates a particular example of the method 400 in which thebrake temperature characteristic criterion is determined and used inorder to generate the first indication. Blocks 402 a to 402 c shown inFIG. 4b may be performed as part of block 402 of FIG. 4a , e.g. by thefirst controller 302. At block 402 a, the brake temperaturecharacteristic criterion is determined according to the oxidation stateof the brake 200. At block 402 b, it is determined whether thetemperature characteristic of the brake 200 satisfies the braketemperature characteristic criterion. At block 402 b, the firstcontroller 302 receives the temperature characteristic of the brake 200(the source of brake temperature is described in further detailhereafter), for example. The first controller 302 compares thetemperature characteristic of the brake received by the first controller302 to the brake temperature characteristic criterion determined atblock 402 a to determine whether or not the brake temperaturecharacteristic criterion is satisfied, for example. If the braketemperature characteristic criterion is satisfied, the process proceedsto block 402 c.

At block 402 c, the first indication is generated depending upon whetherthe brake temperature characteristic criterion is satisfied. The firstindication is generated if the brake temperature characteristicsatisfies the brake temperature characteristic criterion. On the otherhand, if the brake temperature characteristic criterion is not satisfiedat block 402 b, the method ends and no indication is generated. However,the block 402 b may be performed again when an updated temperaturecharacteristic of the brake is available. If there is a change in thethermal oxidation state of the brake 200, the method according to any ofthe described examples may be repeated.

At block 404, The brake 200 is controlled to be disabled based on thefirst indication generated at block 402 c. For example, the secondcontroller 304 may be configured to receive the first indicationgenerated depending upon whether a brake temperature characteristicsatisfies a brake temperature characteristic criterion. For example, asdescribed, if the first indication is generated, the second controller304 may receive the first indication and may disable the brake 200.

The first controller 302 may be configured to monitor the temperaturecharacteristic of the brake 200, and, if the temperature characteristicof the brake 200 no longer satisfies the brake temperaturecharacteristic criterion, generate a second indication for the brakingsystem 214 that the temperature characteristic of the brake 200 nolonger satisfies the brake temperature characteristic criterion. FIG. 4cis a flow diagram illustrating additional process blocks which may formpart of the method 400. For example, the method 400 may proceed fromblock 404 to block 406. At block 406 the temperature characteristic ofthe brake is monitored. For example, measurements of the temperaturecharacteristic as a function of time may be received by the firstcontroller 302. At block 408, it is determined whether or not thetemperature characteristic of the brake 200 still satisfies the braketemperature characteristic criterion. For example, the first controller302 compares an up to date value of the brake temperature characteristicto the brake temperature characteristic criterion. If the temperaturecharacteristic of the brake no longer satisfies the brake temperaturecharacteristic criterion, at block 410 the second indication that thetemperature characteristic of the brake no longer satisfies the braketemperature characteristic criterion is generated by the firstcontroller 302.

The second controller 304 may be configured to receive the secondindication that the temperature characteristic of the brake no longersatisfies the brake temperature characteristic criterion, and controlthe brake selectively to be enabled or disabled based on the receivedindication. As described previously, the second controller 304 maydisable the brake 200 if it receives the first indication. The secondcontroller 304 may control the brake 200 to be enabled if it receivesthe second indication. At block 412, the brake 200 is controlled to beenabled based on the second indication. For examples, if the brake 200has been disabled and the temperature characteristic of the brake 200 nolonger satisfies the brake temperature characteristic criterion, thesecond controller 304 may change the status of the brake 200 from“disabled” to “enabled”. The brake 200 when enabled may once again becontrolled by the braking system 214 to provide braking responsive to abraking request.

On the other hand, if the brake temperature characteristic criterion isstill satisfied, as determined at block 408, the process returns toblock 406 in order to continue monitoring the temperature characteristicof the brake 200, and blocks 406 and 408 are repeated.

The brake temperature characteristic criterion depends on the oxidationstate of the brake. In the examples described hereafter, the braketemperature characteristic criterion depends on the thermal oxidationstate of the brake 200. Therefore, the brake 200 may be disabled sooneror later (as its temperature increases due to braking) depending on itsthermal oxidation state, as explained in further detail hereafter.Managing braking in this manner, to inhibit thermal oxidation of thebrake 200, may prolong the life of the brake 200.

The temperature characteristic of the brake may include a temperature ofthe brake 200 (i.e. a current temperature). The temperature of the brake200 may specifically be the temperature of the brake discs 202 which maybe composed of CC composites as described. It will be appreciated thatthe temperature of the components composed of CC composites is relevantwhen controlling the brake 200 to inhibit thermal oxidation because thecomponents composed of CC composites undergo thermal oxidation. In someexamples, the temperature characteristic may also include a rate ofincrease of temperature of the brake 200.

The brake temperature characteristic criterion may be satisfied if thetemperature of the brake 200 exceeds a brake temperature threshold. Thefirst controller 302 may be configured such that the higher the level ofthermal oxidation of the brake 200, the lower the brake temperaturethreshold of the determined brake temperature characteristic criterionis. In such examples, if the brake 200 has undergone a large amount ofthermal oxidation, the braking system 214 may disable the brake 200 whenit reaches a lower temperature as compared to a brake with less thermaloxidation.

In some examples, the brake temperature characteristic criterion mayalternatively or in addition include a temperature increase ratethreshold. In such examples, where the temperature characteristicincludes a rate of increase of temperature of the brake 200, the braketemperature characteristic criterion may be satisfied if the rate ofincrease of temperature of the brake 200 exceeds the temperatureincrease rate threshold. The following examples are described in thecontext of the temperature characteristic comprising a temperature ofthe brake 200 and the brake temperature characteristic criterion beingsatisfied if the temperature of the brake 200 exceeds the braketemperature threshold.

In some examples, the thermal oxidation state of the brake 200 may becompared to a predetermined thermal oxidation level. In such examples,if the thermal oxidation state of the brake 200 is below thepredetermined thermal oxidation level, the first controller 302 selectsa first brake temperature characteristic criterion which comprises afirst temperature threshold. The first temperature threshold may berelatively high so that the brake 200 can get relatively hot beforebeing disabled by the braking system 214, but not so hot that there issignificant thermal oxidation for a significant period of time.

For some brakes, it may be expected that thermal oxidation may occur ata relatively low rate at temperatures over 400° C. and at a relativelyhigher rate at temperatures over 750° C. There may not be significantthermal oxidation below 400° C. The first temperature threshold maytherefore be above 400° C. For such brakes, the first temperaturethreshold set at, for example, 600° C. would allow use of the brakes upto a relatively high temperature without the risk of the temperaturereaching a level where there is a relatively high rate of thermaloxidation.

If the thermal oxidation state of the brake 200 is above thepredetermined thermal oxidation level, the first controller 302 mayselect a second brake temperature characteristic criterion whichcomprises a second temperature threshold lower than the firsttemperature threshold. Therefore, when the thermal oxidation state ofthe brake 200 exceeds the predetermined thermal oxidation level, thebrake 200 is disabled at a lower temperature. This is so that when thethermal oxidation state of the brake 200 becomes advanced, it isprevented from being exposed to as high temperatures in order to furtherinhibit thermal oxidation and prolong the life of the brake 200.

In some examples, the second temperature threshold may be 400° C. Insome examples, the second brake temperature characteristic criterion maybe selected based on the difference between the thermal oxidation stateof the brake 200 and the predetermined thermal oxidation level. Forexample, above the predetermined thermal oxidation level, the greaterthe level of thermal oxidation of the brake 200, the lower the secondtemperature threshold may be. For example, the second temperaturethreshold may be a value under 600° C. and may decrease as the thermaloxidation state of the brake 200 continues to increase above thepredetermined thermal oxidation level.

The first controller 302 may determine the brake temperaturecharacteristic criterion by using the thermal oxidation state of thebrake 200 as an input into an algorithm for determining the braketemperature characteristic criterion. The algorithm may take account ofthe physical properties of the brake 200. For example, it may be thecase that the brake 200 undergoes thermal oxidation at a high rate belowa temperature of 750° C. In such an example, the first temperaturethreshold may be set lower than 600° C. The first controller 302 mayimplement instructions stored on a computer readable storage medium(e.g. one included in the computing system 106) to perform thealgorithm. In some examples, the first controller 302 may access (from acomputer readable storage medium to which it has access) a look-uptable, which stores thermal oxidation states of the brake 200 andcorresponding predetermined brake temperature characteristic criteria.The first controller 302 may determine the brake temperaturecharacteristic criterion using the look-up table. In some examples, thefirst controller 302 may be configured to generate such a look-up tableusing an algorithm of the aforementioned kind.

As described, thermal oxidation of the brake discs 202 may occur at hightemperatures. The brake 200 of the aircraft 100 may need to be servicedor replaced once the oxidation state of the brake 200 reaches a certainlevel to ensure safe functioning. As described, the brake 200 of theaircraft 100 may need to be serviced or replaced if the oxidationthreshold is reached. The predetermined thermal oxidation level may beset at a value below the oxidation threshold to inhibit thermaloxidation as the thermal oxidation state of the brake 200 approaches theoxidation threshold (e.g. 4% to 6.5% of the original mass of the brake200 lost).

In order to compare the temperature characteristic of the brake 200 tothe determined brake temperature characteristic criterion and to monitorthe temperature characteristic of the brake 200, the first controller302 may receive information regarding the temperature characteristic ofthe brake 200 from a temperature sensor 216 associated with the brake200 (see FIG. 2). The temperature sensor 216 may be provided in thermalcontact with one of the brake discs. In the example of FIG. 2, thetemperature sensor 216 is provided on the stator 210. In this example,the stator 210 is the brake disc likely to reach the highesttemperatures. The temperature sensor 216 may be any type of temperaturesensor suitable for use in an aircraft brake assembly. For example, thetemperature sensor 216 is able to function properly at the temperatureranges likely to be reached by the brake discs 202. For example, thetemperature sensor 216 may be a thermocouple, a surface acoustic wave(SAW) sensor, an eddy current sensor, a resistance thermal sensor, astrain gauge, or the like. The first controller 302 may receive braketemperature measurements from the temperature sensor 216 via a wired orwireless communication link. If a temperature sensor is provided on apart of the brake 200 other than on one of the brake discs 202, thetemperature of the brake discs 202 may be determined using an indicationof the relationship between a temperature measured by said temperaturesensor and the temperature of the brake discs 202. In some examples, theindication of the relationship may be determined by experiment. In someexamples, the indication of the relationship may be determined using abrake thermal model.

The first controller 302 may receive brake temperature measurements fromthe temperature sensor 216 in real-time. The first controller 302 maycontinuously receive brake temperature measurements, or alternativelymay periodically receive discrete items of brake temperatureinformation. In some examples, the controller 302 may request braketemperature measurements from the temperature sensor 216 and receivebrake temperature measurements in response. A rate of increase oftemperature of the brake 200 may be determined based on at least twomeasurements of the temperature at different times.

The first controller 302 may receive a predicted temperaturecharacteristic from a brake temperature prediction function as thetemperature characteristic of the brake 200. The brake temperatureprediction function may predict the temperature of the brake 200 basedon the energy input into the brake 200 during a braking event. A brakingevent is, for example, an event comprising one or more applications ofthe brake 200. Using the energy input into the brake 200, the mass ofthe brake 200 and the specific heat capacity of the brake 200, a changein temperature of the brake 200 caused by the input energy can bedetermined. The temperature of the brake 200 may then be determinedusing the temperature change, i.e. by adding it to an initialtemperature of the brake 200. The initial temperature before the brakingevent may be known from previous iterations of such a calculation. Onthe other hand, if the energy input is due the first brake applicationof the day (i.e. the brake 200 has not been applied for a significantamount of time), the initial temperature may be taken to be theenvironmental temperature.

In some examples, the brake thermal model (e.g. a computational fluiddynamics model) may be used to predict a temperature of the brake 200given an amount of energy input into the brake 200. For example, thephysical properties of the brake 200 (e.g. mass, heat capacity, etc.),environmental characteristics and the energy input into the brake 200may be input into the brake thermal model, and the brake thermal modelmay output a predicted temperature of the brake 200. The environmentalcharacteristics may include ambient temperature (e.g. in the vicinity ofthe brake 200), wind conditions, or other characteristics which mayaffect the temperature of the brake 200. The environmentalcharacteristics may be measured by instruments included in instruments108, for example.

In some examples, the rate of increase of temperature of the brake 200may be predicted based on the energy input into the brake 200 by thebrake temperature prediction function. For example, the rate of increasemay be predicted based on the energy input into the brake and thephysical properties of the brake 200 using the brake thermal model.

As described, the thermal oxidation state of the brake 200 is related tothe amount of mass of the brake 200 lost due to thermal oxidation whichmay be taken into account when determining the mass of the brake 200.The mass lost due to wear of the brake discs 202 may also be taken intoaccount. For example, the instruments 108 may comprise a brake wearsensor associated with the brake 200. The brake wear sensor may providean indication of a reduction in length L of the brake discs 202. Usingthe reduction in length L due to wear, a reduction in the mass of thebrake 200 due to wear may be determined. In some examples, the mass ofthe brake 200 may be determined by subtracting the amount of mass lostdue to thermal oxidation and the amount of mass lost due to brake wearfrom the initial mass of the brake 200 (e.g. as specified by the brakemanufacturer or measured at installation of the brake 200 into aircraft100).

The energy input into the brake 200 may be determined using measurementsfrom instruments included in instruments 108. The instruments 108 mayinclude a torque sensor for measuring the torque reacted by the brake200 and a tachometer for measuring the rotational speed of the wheel104. In such examples, the energy input into the brake 200 is calculatedby integrating the product of the wheel speed and torque over time.

The first controller 302 may receive a predicted temperature if, forexample, the temperature sensor 216 malfunctions or the first controller302 is not able to receive brake temperature measurements from thetemperature sensor 216. In some examples, a processor (e.g. a processorof the computing system 106) may determine whether to provide the firstcontroller 302 with a brake temperature measurement from the temperaturesensor 216 or a predicted temperature from the brake temperatureprediction function. In some examples, the first controller 32 mayreceive a brake temperature measurement from the temperature sensor 216and a predicted temperature from the brake temperature predictionfunction, and determine which temperature value to use. For example, ifthere is a large discrepancy in the two values, the temperature valueclosest to what might be expected given the mass, speed, etc. of theaircraft 100 may be used.

During use of the aircraft 100, there may be instances where it is notdesirable to have one or more of the brakes of the aircraft 100disabled. For example, it may be desired that all the brakes are usedduring landing to reduce the speed of the aircraft 100. The secondcontroller 304 may be configured to disable a brake if a taxiingcriterion is met. In such examples, brake 200 may only be disabledresponsive to the second controller 304 receiving the first indicationduring a taxiing phase as defined by the taxiing criterion.

The taxiing criterion may comprise one or more of an aircraft speedthreshold and a particular flight phase of the aircraft 100. Theaircraft speed threshold may be defined such that an aircraft speed lessthan or equal to the aircraft speed threshold satisfies the taxiingcriterion. For example, the aircraft speed threshold may be 30 knots. Insuch examples, the second controller 304 does not disable the brake 200upon receiving the first indication if the speed of the aircraft isabove 30 knots. This is because, at higher speeds a greater brakingforce may be required to reduce the speed of the aircraft 100 within acertain time or distance. The second controller may receive informationrelating to the aircraft speed from an on-board instrument (i.e. aninstrument included in instruments 108), or a processor of the computingsystem 106.

The particular flight phase may be indicated by a flight phaseindication system of the aircraft 100. The particular flight phase maybe the taxiing phase after landing and/or the taxiing phase beforetake-off, for example. The flight phase indication system may beimplemented at least in part by the computing system 106 of the aircraft100. In such examples, the second controller 304 does not disable thebrake 200 unless the flight phase is indicated to be the taxiing phaseafter landing and/or the taxiing phase before take-off. By disabling thebrake 200 responsive to the first indication only when the aircraft isin a taxiing phase as defined by the taxiing criterion, the brake 200 ismade available to provide braking during other phases in which reducingthe speed of the aircraft 100 is a higher priority than protecting thebrake 200 against thermal oxidation.

As described, the braking system 214 causes the brake 200 to be appliedin response to a braking request. The second controller 304 of thebraking system 214 may be configured to receive a braking request when apilot of the aircraft 100 presses a brake pedal. The braking request maycomprise information relating to a requested braking intensity. Forexample, the braking request may include information about how hard/farthe pilot has pressed the brake pedal.

In some cases, a significant amount of braking may be required. Forexample, the pilot may press the brake pedal hard to bring the aircraft100 to an immediate stop or to significantly reduce the aircraft speedin a short amount of time. In such cases, it may not be desired to haveany of the brakes of the aircraft 100 disabled so that sufficientbraking can be provided. The second controller 304 may determine, basedon the information related to the requested braking intensity, whetherthe requested braking intensity exceeds a braking intensity threshold.If the requested braking intensity exceeds the braking intensitythreshold, the second controller 304 may enable at least one disabledbrake. For example, if the brake 200 has been disabled responsive to thefirst indication, the second controller 304 may enable the brake 200 inresponse to the requested braking intensity exceeding the brakeintensity threshold.

FIG. 5 is a flow diagram illustrating a method 500 performed by thesecond controller 304 of enabling a disabled brake in response to abraking request with high braking intensity. At block 502, a brakingrequest comprising information related to the requested brakingintensity is received. For example, as described, the second controller304 receives the braking request. At block 504, the second controller304 determines, based on the information related to the requestedbraking intensity, whether the requested braking intensity exceeds thebraking intensity threshold. If the requested braking intensity exceedsthe braking intensity threshold, the method 500 proceeds to block 506and at least one disabled brake is enabled. For example, if the brake200 has previously been disabled responsive to the first indication, thebrake 200 may be enabled by the second controller 304 at block 506. Inthis manner, depending on the requested braking intensity, the brake 200may again be enabled to provide braking if relatively high brakingintensity is required.

On the other hand, if the requested braking intensity does not exceedthe braking intensity threshold, the method 500 ends. The method 500 maybe repeated each time a braking request is made so that the requestedbraking intensity can be provided.

All or part of the described methods may be performed in real-time,during aircraft operation. For example, the described methods may beperformed in real-time when the aircraft 100 is in a taxiing phaseand/or when a braking event is occurring. For example, the temperaturecharacteristic of the brake 200 may be compared to the brake temperaturecharacteristic criterion repeatedly. For instance, the first controller302 may repeatedly determine whether the temperature characteristic ofthe brake 200 satisfies the brake temperature characteristic criterionduring a braking event. The second controller 304 may control the brake200 as described in real-time based on this determination. For example,the second controller 304 may receive an indication each time the braketemperature characteristic criterion is determined to be satisfied or nolonger satisfied (i.e. the second control 304 may receive first andsecond indications, as appropriate, in real-time) and control the brake200 selectively to be enabled or disables depending on the receivedindications.

For example, all or part of the described methods may be performedrepeatedly at a fast rate, with the temperature of the brake 200 beingsampled multiple times per second, up to the sampling rate of thetemperature sensor.

FIG. 6 summarizes an exemplary method 600 of determining a thermaloxidation state of a brake, such as the brake assembly 200, of anaircraft landing gear assembly 102. The method 600 involves determininga thermal oxidation state of the brake assembly 200 after a brakingevent, using a thermal oxidation model based on an initial thermaloxidation state (which may also be referred to as the initial thermaloxidation level) before the braking event and a temperature profile ofthe brake with respect to time. The determined thermal oxidation stateof the brake assembly 200 after the braking event may be referred to asan updated thermal oxidation state. This is because the thermaloxidation state of the brake assembly 200 after the braking event takesaccount of the change in the initial thermal oxidation state due to thebraking event.

The braking event is an event relating to the application of the brakeassembly 200. For example, a braking event may comprise one or moreapplications of the brake assembly 200 to slow or stop the aircraft 100.In some examples, the braking event may be a part of a time during whichthe brake assembly 200 is continuously being applied. Any time the brakeassembly 200 is applied, the temperature of the brake assembly 200 mayrise. This is because when brake assembly 200 is applied to reduce thespeed of the aircraft 100, some of the kinetic energy of the aircraft100 is absorbed into the brake assembly 200 as heat causing itstemperature to rise. Therefore, whether or not the brake assembly 200has been applied can be determined based on temperature variations ofthe brake assembly 200.

At block 602 of the method 600, the temperature profile and the initialthermal oxidation state of the brake assembly 200 are input. Asexplained above, the temperature profile indicates a variation oftemperature with time. The input temperature profile may, for example,relate to a use cycle of the aircraft 100. For example, the temperatureprofile may be for an entire use cycle of the aircraft 100, e.g. thetime from when the aircraft 100 is at a departure gate before a flightto when the aircraft 100 is at an arrival gate after a flight.Specifically, the temperature profile may indicate the variation oftemperature over time for all braking events that take place during acycle. In other examples, the temperature profile may not be for anentire use cycle of the aircraft 100. For example, the temperatureprofile may be over a single braking event, or a part of a cycle withmany braking events. In some examples, a number of temperature profilesbelonging to a particular use cycle may be used to determine the thermaloxidation state of the brake assembly 200 after that use cycle.

The temperature profile may, for example, relate to a use cycle that hasoccurred. In other words, the temperature profile may include actualdata from the temperature sensor 216 of the aircraft 100 during aprevious use cycle. In such examples, the temperature profile relates toreal data. On the other hand, in some examples, the temperature profilemay be a predicted temperature profile of a predicted future use cycleof the aircraft 100. In that context, a braking event may be a predictedfuture braking event.

The initial thermal oxidation state of brake assembly 200 is the thermaloxidation state of the brake assembly 200 before the braking event forwhich the updated thermal oxidation state is being determined. Forexample, for a new brake assembly 200 installed in aircraft 100, theinitial oxidation state may indicate no oxidation. In some examples, theinitial oxidation state for a newly installed brake assembly 200 may beset at installation by aircraft maintenance personnel and may eitherindicate no oxidation or some oxidation as assessed by the person(s)performing the installation. In examples where the brake assembly 200 isnot new, the initial oxidation state may be the oxidation statecalculated at a previous instance of method 600 being performed. In someexamples, a brake or a brake component which is not new may be installedon aircraft 100. If the temperature profile information for all previousbraking events involving that brake or brake component is available, thethermal oxidation state at installation may be determined using theavailable temperature profile information using method 600, or by othermethods disclosed herein.

At block 604 of method 600, a thermal oxidation state after the brakingevent (updated thermal oxidation state) is determined using a thermaloxidation model. For example, a thermal oxidation model is applied basedon the input temperature profile and the initial thermal oxidation stateof the brake assembly 200. A thermal oxidation model, for example,indicates how the thermal oxidation state is expected to change withtime for various temperatures starting from the initial thermaloxidation state. A thermal oxidation model is a model of the evolutionof the thermal oxidation of the brake. Which thermal oxidation model isused may depend, for example, on the initial thermal oxidation state.The details and selection of appropriate thermal oxidation models isdescribed further below. In some examples, the method 600 may beperformed live during a use cycle of the aircraft 100. In the case ofthe method 600 being performed live (i.e. in real time or near realtime), the temperature profile used may be from the temperature dataacquired thus far by the temperature sensor 216, for example. At block604, therefore, it is determined how the oxidation state, starting fromthe initial oxidation state, has changed as a result of the increasedtemperature associated with the braking event in question.

After the updated thermal oxidation state has been determined, theinitial thermal oxidation state may be set to the updated thermaloxidation state. In this way, the initial thermal oxidation state iskept up to date with all previous braking events. In examples where thetemperature profile relates to more than one braking event, the method600 may be performed again in order to determine an updated thermaloxidation state after a subsequent braking event. Updating the initialthermal oxidation state in this manner may ensure that the initialthermal oxidation state being used for a subsequent braking eventaccounts for all the previous braking events.

In examples where the temperature profile for an entire use cycle of theaircraft 100, the method 600 may be performed to determine respectiveupdated thermal oxidation states after each braking event within thatuse cycle. It will be understood that this process may be carried outsequentially in relation to the chronology of the braking events. Thisis so that the determination of the updated thermal oxidation state foreach of the braking events is done from a starting point (an initialthermal oxidation state) which takes account of all previous brakingevents.

In the method 600, the updated thermal oxidation state after a brakingevent may, for example, be determined based on a high temperatureinterval, the initial thermal oxidation state and a thermal oxidationrate parameter, using an appropriate thermal oxidation model.

FIG. 7 is a flow diagram of a method 700 showing acts that may beperformed as part of method 600. For example, the method 700 involvesmore specific examples of the block 604 of the method 600. Block 702 isidentical to block 602 of the method 600, in that a temperature profileof the brake with respect to time and the initial thermal oxidationstate of the brake assembly 200 are input. At block 704, the temperatureprofile is compared to a set of temperature criteria. The set oftemperature criteria may include a set of temperature thresholds. Forexample, the set of temperature criteria may include a first temperaturethreshold of 400° C. and a second temperature threshold of 750° C. Inother examples, different temperature thresholds may be used dependingon the physical properties of the brake assembly 200. The comparison ofthe temperature profile may, for example, take place sequentially intime order of the temperature data contained in the temperature profile.For example, a temperature value may be compared to the set oftemperature thresholds, and subsequently, the next temperature value intime may be compared to the set of temperature thresholds.

At block 706, it is determined if one or more of the temperaturecriteria are met. If, for example, none of the temperature thresholdsare exceeded, the method 700 ends. It will be appreciated that thermaloxidation of the CC composite of the brake discs 202 is a process thatis most significant at high temperatures. A comparison of thetemperature profile with the set of temperature thresholds thereforeidentifies high temperature events corresponding to braking events thatmay result in thermal oxidation. As mentioned above, a braking event is,for example, an application of the brake assembly 200. However, a hightemperature event is an event during which the temperature of the brakeassembly exceeds at least one of the temperature thresholds as a resultof a braking event. For example, if during a braking event (i.e. abraking application) the temperature of the brake assembly 200 remainsbelow all temperature thresholds, then no high temperature eventsoccurred during that braking event. On the other hand, if during abraking event the temperature of the brake assembly exceeds atemperature threshold, the part of the braking event for which thattemperature threshold is exceeded may be referred to as a hightemperature event. If more than one temperature threshold is exceeded, ahigh temperature event may be the part of the braking event for whichthe highest temperature threshold is exceeded.

The temperature thresholds may be set based on temperatures above whicha significant amount of thermal oxidation is expected to occur.Therefore, the method 700 ends if none of the temperature thresholds areexceeded. This is because, in this example, no braking events causing asufficiently high temperature for thermal oxidation have occurred. Insuch examples, the updated thermal oxidation state after the brakingevent may simply be set to the initial thermal oxidation state beforethe braking event in question.

On the other hand, if at least one of the temperature thresholds isexceeded, at block 708 of the method 700, a high temperature eventcorresponding to the braking event in question is identified. A hightemperature event corresponds to the part of the temperature profilewhich is above the highest of the exceeded temperature thresholds. Thisis because the part of the temperature profile which is above thehighest of the exceeded thresholds corresponds to the part of thebraking event for which the highest temperature threshold is exceeded.The identification of a high temperature event is described withreference to FIG. 8. FIG. 8 is a graph illustrating a part of an exampletemperature profile. In the graph of FIG. 8, the vertical axisrepresents temperature of the brake assembly 200, and the horizontalaxis represents time. In this example, profile part 802 indicates thatthe temperature of the brake assembly 200 exceeds a first temperaturethreshold 804 and a second temperature threshold 806. In this example,the high temperature event is identified as the part of the profile 802above the second temperature threshold 806 as the second temperaturethreshold 806 is the highest temperature threshold which is exceeded.

The amount of thermal oxidation which occurs above the secondtemperature threshold 806 may be significantly greater for a giveninterval of time compared to the thermal oxidation above the firsttemperature threshold 804 but below the second temperature threshold806. Therefore, in this example, the parts of the temperature profilebelow the second temperature threshold 806 are not taken into account.In other examples, for example when the method 700 is used for liveoxidation state monitoring as described further below, the parts of thetemperature profile between the two temperature thresholds may be takeninto account. It should be appreciated that the graph of FIG. 8 ismerely an illustration of an example for explanatory purposes.

At block 710, the interval of time taken by the high temperature eventis determined to be the high temperature interval. As mentioned above,the updated thermal oxidation state may be determined based on (amongother factors) the high temperature interval. In the example of FIG. 8,the high temperature interval is determined to be the time interval 808.

At block 712, a high temperature event value of the brake assembly 200is determined for the high temperature interval. The high temperatureevent value is a value of temperature ascribed to the high temperatureevent. In some examples, the high temperature event value is the averagetemperature during the high temperature interval. Alternatives to thehigh temperature event value being the average temperature are describedbelow in the context of live oxidation monitoring.

At block 714, an oxidation rate parameter is calculated based on thehigh temperature event value and physical characteristic information ofthe brake. For example, the oxidation rate parameter for the thermaloxidation reaction may be determined based on the Arrhenius equationshown as Equation 1 below:

k(T)=Ae ^(−E) ^(A) ^(/RT)  (1)

In Equation 1, k(T) is the thermal oxidation rate, A is apre-exponential constant, E_(A) is the activation energy of the carbonatoms of the CC composite components of brake assembly 200, R is theuniversal gas constant and T is the temperature. In this example, for aparticular high temperature event, the temperature T in Equation 1 isset to the high temperature event value for the purpose of block 714. Inthis example, the thermal oxidation rate k(T) is the oxidation parameterdetermined at block 714. The values of activation energy E_(A), and thepre-exponential constant A may depend on the physical properties of theCC composite components of brake assembly 200 (in this example, thebrake discs 202). For example, the values of these parameters may dependon the density, porosity, manufacturing process, contaminants present inthe CC composite structures, the surface finish of the components andsurface coatings of the brake assembly 200. The values of the activationenergy E_(A), and the pre-exponential constant A may also vary dependingon the high temperature event value and the initial thermal oxidationstate. Therefore, in order to determine the oxidation parameter,appropriate values of activation energy E_(A), and the pre-exponentialconstant A may be selected based on the physical properties of the brakeassembly 200, the high temperature event value and the initial thermaloxidation state before the braking event in question.

For example, the activation energy E_(A) may be related inversely totemperature. The activation energy E_(A) may become lower at atemperature at which oxygen molecules are able to penetrate past thesurface of the brake discs 202 and oxidation of carbon deeper in thebrake discs 202 can take place. The appropriate values of activationenergy E_(A), and the pre-exponential constant A may, for example, bedetermined experimentally for different initial thermal oxidationamounts, temperatures and physical properties of the brake beingconsidered before the method 700 is implemented.

FIG. 9 is a graph of an example of the evolution with time of thermaloxidation of the brake discs of a brake assembly 200 for a specifictemperature. The vertical axis of the graph in FIG. 9 represents ameasure of the thermal oxidation indicated by the thermal oxidationstate Ox. For example, the thermal oxidation state Ox may be theproportion of mass of the brake assembly 200 lost due to thermaloxidation of the brake discs 202. The evolution curve 902 shows how theproportion of mass lost due to thermal oxidation advances with time atthe specific temperature. It should be noted that a different evolutioncurve would indicate the variation of the thermal oxidation state Oxover time for a different temperature value.

In this example, the thermal oxidation state Ox advances with timedifferently below a thermal oxidation state level 904, than it doesabove the thermal oxidation state level 904. The thermal oxidation stateOx (i.e. mass lost due to thermal oxidation) is shown to increasenon-linearly with time below oxidation state level 904 and substantiallylinearly with time above oxidation state level 904, in this example. Inthis example, the thermal oxidation state increases at an acceleratedrate with time until thermal oxidation state level 904 is reached. Afterthermal oxidation state level 904 is reached, the rate of change ofthermal oxidation state Ox with time remains generally constant. Thepart of the graph of FIG. 9 below thermal oxidation state level 904 maybe considered as a first thermal oxidation zone, namely Zone 1, and thepart of the graph of FIG. 9 above thermal oxidation state level 904 maybe considered as a second thermal oxidation zone, namely Zone 2, forexample.

In some examples, different values of the activation energy E_(A), andthe pre-exponential constant A may be used depending on which thermaloxidation zone the brake assembly 200 is in as indicated by the initialthermal oxidation state.

At block 716, a thermal oxidation model is selected based on the initialthermal oxidation state before the braking event. The thermal oxidationmodel describes the evolution of the thermal oxidation state Ox of thebrake assembly 200 for different values of temperature. A thermaloxidation model which describes the evolution of the thermal oxidationstate Ox in Zone 1 may be selected when the initial thermal oxidationstate is in Zone 1. A thermal oxidation model which describes theevolution of the thermal oxidation state Ox in Zone 2 may be selectedwhen the initial thermal oxidation state is in Zone 2. For example, afirst thermal oxidation model, Model 1, may be selected for Zone 1, anda second thermal oxidation model, Model 2, may be selected for Zone 2.Model 1 for Zone 1, describing the non-linear change of thermaloxidation state Ox with time, may be represented by Equation 2. Model 2for Zone 2, describing the linear change of thermal oxidation state Oxwith time, may be represented by Equation 3 below.

Ox=1−[1−{k(T)×t _(eq)(1−n)}^(1/) ^(1-n) ]  (2)

Ox=k(T)×t _(eq)  (3)

In Equation 2 and Equation 3 above, k(T) is the thermal oxidation rateas defined by Equation 1. The parameter t_(eq) is the equivalent time,which is the time it would take, at temperature T, to reach the thermaloxidation state Ox. The parameter n is referred to as the equation orderand depends on the properties of the CC composite used in the brakeassembly 200. The parameter n may, for example be experimentallydetermined for a brake using a particular CC composite.

In some examples, different thermal oxidation models to those describedby Equations 2 and 3 may be used. In some examples, a single thermaloxidation model may be used which describes the evolution of the thermaloxidation state Ox for all thermal oxidation states Ox that are relevantto the brake assembly 200. In some examples, more than two thermaloxidation models may be used for respective ranges of thermal oxidationstates Ox. The method 700 may be modified appropriately in order to usesuch alternative thermal oxidation models. For example, a different setof inputs may be applied to the thermal oxidation model, as appropriate,than are described in this specific example of the method 700.

It will be understood that block 716 may be performed at any stage ofthe method 700 once block 702 has been performed, because block 716requires the initial thermal oxidation state.

At block 718, the updated thermal oxidation state for the hightemperature event is determined using the selected thermal oxidationmodel based on the high temperature interval, the initial thermaloxidation state and the determined thermal oxidation rate parameter. Forexample, the time it would take to reach the initial thermal oxidationstate from zero at the high temperature value is determined and the hightemperature interval is added to this time in order to determine thevalue of t_(eq) to be used in the selected thermal oxidation model.Inputting the thus determined value of t_(eq), as well as the thermaloxidation parameter into the equation selected from Equations 2 and 3above results in, as an output, the updated thermal oxidation state ofthe brake assembly 200 after the high temperature event.

The updated thermal oxidation state may be set to the new initialthermal oxidation state for a subsequent use of the method 700 for asubsequent high temperature event in the temperature profile.

In some examples, the method 600 and/or 700 may be performed live duringa use cycle when braking events are taking place. In such examples, partof the method 700, for example, may be modified to allow live brakeoxidation monitoring, and the temperature profile may correspond totemperature values being measured live. For example, temperatureinformation which the temperature sensor 216 provides may continuouslybe compared to the set of temperature criteria as per block 704 ofmethod 700, and high temperature events may be identified substantiallyas they occur. It will be understood that even though this kind ofoxidation state monitoring is described as live, the extent to which itoccurs in real time will depend on various hardware and software (e.g.processing speed) limitations. For example, there may be a time delaybetween temperature values corresponding to a high temperature eventbeing measured by the temperature sensor 216, and those values resultingultimately in updated thermal oxidation states of the brake assembly200.

For example, high temperature events may be identified as smaller partsof the temperature profile than in the example described above.Referring again to FIG. 8, the part of the profile part 802 occurringwithin the time interval indicated as 810 may be taken to be a hightemperature event and the interval 810 as its high temperature interval.In this example, the high temperature event value may be taken to be thetemperature measured at the beginning or the end of the high temperatureinterval 810, for example, or the average of the two temperature values.Unlike the above example, in the case of live monitoring, parts of thetemperature profile between the first and second temperature thresholdsmay be taken into account even when the temperature exceeds the secondtemperature threshold 806. In the case of live monitoring, any part ofthe temperature profile above at least one temperature threshold, suchas the part identified by interval 810, may be identified as a hightemperature event. It will be understood that such modifications mayallow the thermal oxidation state of the brake assembly 200 to beupdated as high temperature events corresponding to braking events aretaking place. In some examples, high temperature events may beidentified based on the time between subsequent temperature measurementstaken by the temperature sensor 216. For example, the interval 810 maybe the interval of time between subsequent temperature measurementstaken by the temperature sensor 216.

The methods 600 and 700 may be used in order to determine the thermaloxidation state of the brake assembly 200 after an actual use cycle ofthe aircraft 100 or in a live manner during an actual use cycle. In suchexamples, this may be done based on one or more temperature profilesencompassing braking events within that use cycle. As mentioned above,in some examples, the thermal oxidation state of the brake assembly 200is determined in respect of a use cycle which has actually occurredusing temperature profile information collected by the temperaturesensor 216.

On the other hand, in some examples, the method 600 or 700 may be usedto predict a future thermal oxidation state of the brake assembly 200after a first plurality of predicted future use cycles of the aircraft100. The first plurality of future use cycles may be a number of cyclesafter which a thermal oxidation threshold is reached. Each predictedfuture use cycle may include a respective plurality of braking events.For each predicted future use cycle, the predictions may be based on arespective predicted temperature profile of the brake assembly 200 and acurrent thermal oxidation state. The current thermal oxidation state is,for example, the oxidation state taking into account all the previousbraking events experienced by the brake assembly 200.

For example, the predicted temperature profiles may be input into themethod 600 or 700, for example in time order, to determine the futurethermal oxidation state of brake assembly 200. The predicted temperatureprofile of a predicted future use cycle may be predicted based onprevious temperature profiles for previous actual use cycles of theaircraft 100. For example, using the parts of previous temperatureprofiles relating to the landing phase, landing phase parts of thetemperature profile for a future use cycle may be predicted. For thepurpose of predicting a future thermal oxidation state, high temperatureintervals, high temperature event values, etc. may be stored in acomputer readable storage medium when the method 600 or 700 is beingcarried out for actual use cycles of aircraft 100.

In some examples, data from previous cycles may not be available, forexample, because brake the assembly 200 may be new. In some examples,enough data may not be available to reliably predict temperatureprofiles for predicted future use cycles. In such examples,predetermined temperature profiles may be used. The predeterminedtemperature profiles may be profiles typically expected for the futureuse cycle of aircraft 100.

The predicted temperature profiles may, for example, take into accountthe future flight schedule of the aircraft 100. For example, theaircraft 100 may be expected to land at an airport with a short runwayrequiring high energy (i.e. high temperature) braking upon landing forsome of its predicted future use cycles. For those predicted future usecycles, the predicted temperature profiles may indicate high energybraking upon landing. It will be appreciated that various other factorsmay be taken into account when predicting temperature profiles such astaxiing time at various phases of a predicted future use cycle, waitingtime between a taxiing phase and the preceding landing phase, and thelike.

As mentioned above, the first plurality of predicted future use cyclesmay be a number of predicted future cycles after which the predictedfuture thermal oxidation state reaches a thermal oxidation threshold.For example, the prediction of the future thermal oxidation state maystop after a cycle in which the thermal oxidation threshold is reached.In some examples, the prediction of the future thermal oxidation statemay stop as soon as the thermal oxidation threshold is reached. Thethermal oxidation threshold may be an oxidation state at which servicingor replacement of the brake assembly 200 or a component of the brakeassembly 200 is required. For example, the brake assembly 200 mayrequire a service if its mass is reduced by between 4% and 6.5%, forinstance 5.7%, where the selected percentage threshold may varydepending, for instance, on the original, manufactured disc density. Inthis example, the first plurality of predicted future use cycles is thenumber of cycles it takes for the proportion of mass lost due to thermaloxidation to reach or exceed, for instance, 5.7% (i.e. being within therange 4% to 6.5%).

On the other hand, in some examples, the prediction of the futurethermal oxidation state may stop at the end of a predicted future usecycle during which the future thermal oxidation state approaches closeto the thermal oxidation threshold such that the future thermaloxidation state can be expected to reach the thermal oxidation thresholdduring the next predicted future use cycle. In such examples, thethermal oxidation threshold may be considered reached within the firstplurality of predicted future use cycles. This is because, in reality,an aircraft 100 with a brake assembly 200 expected to reach the thermaloxidation threshold in a strict sense in the very next cycle would notbe permitted to fly and a service or replacement relating to the brakeassembly 200 may take place at that point.

Using the first plurality of predicted future use cycles, an indicationmay be given as to how many use cycles can take place before the brakeassembly 200 or a component of the brake assembly 200 requires servicingor replacement due to thermal oxidation. In the examples where thethermal oxidation threshold is strictly reached or exceeded during thelast of the first plurality of future cycles, the number of cyclesbefore a service or replacement is required due to thermal oxidation maybe predicted as one fewer than the number of cycles in the firstplurality. In examples where the prediction of the future thermaloxidation state stops when the thermal oxidation threshold is expectedto be reached in the next cycle after the first plurality, the firstplurality is taken as the number of cycles before a service orreplacement due to thermal oxidation is required.

FIG. 10 is a flow diagram of a method 1000 of determining an amount ofbrake wear caused by a braking event, using a brake wear model based onan amount of energy absorbed by the brake assembly 200 due to thebraking event and a density parameter of the brake assembly 200. Theamount of brake wear may be determined for all braking events whereenergy is input into the brake assembly 200 in a process involvingfriction that would cause a surface of the brake discs to wear. Forexample, wear of the brake discs due to friction may cause the length ofthe brake discs 202 (length L as shown in FIG. 2) to decrease as brakedisk material is lost by the action of friction.

For example, the amount of brake wear may be determined for thosebraking events which do not involve any high temperature events. For themethod 1000, a braking event may, for example, be identified based onthe temperature profile as an event where the temperature of the brakeassembly 200 increases. In some examples, a braking event may simply beidentified based on an indication that brake assembly 200 has beenapplied. For example, the computing system 106 of the aircraft 100 maydetect when brake assembly 200 is applied and released.

At block 1002 of the method 1000, the energy input into the brakeassembly 200 during the braking event is determined. The energy inputinto the brake assembly 200 may, for example, be determined based on thecharacteristics of the aircraft 100 during the braking event, such as amass of the aircraft 100, the velocity of the aircraft 100 during thebraking event, etc. The energy absorbed by the brake assembly 200 can becalculated based on such characteristics of the aircraft 100 bydetermining the kinetic energy of the aircraft 100. For example, a givenproportion of the kinetic energy of the aircraft 100 may be absorbed bythe brake assembly 200 to reduce the kinetic energy of the aircraft 100.In some examples, the energy input into the brake assembly 200 may bedetermined based on measurements acquired by the instruments 108 of theaircraft 100. For example, the instruments 108 may include a tachometerassociated with the wheel 104 to which the brake assembly 200 isassociated. In such examples, the tachometer measures the rotationalspeed of the wheel 104, and the energy absorbed by the brake assembly200 can be determined using the change of the rotational speed withrespect to time.

In other examples, if the mass of the brake assembly 200 is known, theenergy absorbed may be determined based on the increase in temperatureof the brake assembly 200 taking into account the specific heat of thebrake assembly 200. In some examples, the mass of the brake assembly 200may be determined based on the thermal oxidation state of the brakeassembly 200 determined according to the above described methods,because, as described above, the thermal oxidation state may beexpressed as an amount of mass lost from brake assembly 200 due tothermal oxidation.

At block 1004 of the method 1000, a density parameter of the brakeassembly 200 is determined. The density parameter, for example, is aparameter indicating the decrease in density of the brake assembly 200compared with the original density, taking into account lost mass. Thedensity of the brake assembly 200 may decrease, for example, due tothermal oxidation. It will be understood that thermal oxidation causes areduction in mass because carbon atoms react with oxygen to form carbondioxide or carbon monoxide and are thus removed from brake discs 202.However, thermal oxidation may not necessarily change the volume of thebrake discs 202. This is because thermal oxidation may not act uniformlyon a particular surface of a brake disc and may take place up to acertain depth inside the brake disc.

The density parameter may be expressed as (1-Ox) where the thermaloxidation state Ox is expressed as a number between zero and one. Forexample, the density of the brake assembly 200 is reduced by a factor(1-Ox) compared to the initial density before any thermal oxidation tookplace (i.e. when the brake assembly 200 was new). Therefore, the densityparameter may be determined based on the initial oxidation state beforethe braking event.

In some examples, the reduced density of the brake assembly 200 may bedetermined based on measurements by instruments included in theinstruments 108. For example, the mass of the brake assembly 200 may becalculated based on an amount of energy absorbed by the brake assembly200 (based on measurements from a tachometer, for example) and theconsequent increase in its temperature (based on measurements fromtemperature sensor 216, for example). The reduced density of the brakeassembly 200 may be determined based on the calculated mass of the brakeassembly 200. The aircraft 100 may include a wear pin associated withbrake assembly 200. Typically, a wear pin provides an indication of thereduction in length L of a brake and therefore an indication of thebrake wear. The wear pin may be checked between cycles by ground crew,for example, and an updated volume value of the brake assembly 200acquired. In some examples, there may be other ways to measure thechange in length L of the brake assembly 200. For example, a lengthsensor may be provided for the brake assembly 200, and/or electricallyactuated brakes may be used. An updated volume value may be determined,based on reduced length L, and used to determine the reduced densityfrom the mass. During a single cycle, the change in volume of brakeassembly 200 may be insignificant for the purpose of calculating thedensity parameter, and an updated volume may be acquired after a numberof cycles. From the reduced density, the density parameter may bedetermined.

At block 1006 of the method 1000, an amount of brake wear caused by thebraking event is determined, using a brake wear model based on theenergy absorbed by the brake assembly 200 and the density parameter fromblock 1004. For example, the mass of the brake assembly 200 lost due towear during the wear event is determined using the brake wear model ofEquation 4 below.

$\begin{matrix}{m_{wear} = \frac{W + {X \times E_{brake}} + {Y \times E_{brake}^{2}} + {Z \times E_{brake}^{2}}}{\left( {1 - {Ox}} \right)}} & (4)\end{matrix}$

In Equation 4 above, m_(wear) is the mass lost due to wear during thebraking event, E_(brake) is the energy absorbed by the brake assembly200, and W, X, Y and Z are constants. The constants W, X, Y and Z may,for example, be determined by experiment beforehand, and may varydepending on the properties of the brake assembly 200. The brake wearamount for a braking event may be determined as a reduction in length Lof the brake assembly 200 based on the reduction of mass due to brakewear during that braking event.

As mentioned above, the initial thermal oxidation rate is used todetermine the density parameter in some examples. In these examples,when a braking event takes place during which a high temperature eventalso occurs, the initial thermal oxidation state may be used for thedetermination of block 1006. This is because brake wear occurs on a muchshorter timescale than thermal oxidation.

The amount of brake wear determined for a braking event may be added tothe amount of brake wear from all previous braking events of the brakeassembly 200 in order to determine the total brake wear amount.

The method 1000 may, for example, be performed live during a time whenbraking events are taking place, or for a use cycle which has alreadyoccurred using the relevant data from that use cycle. The method 1000may also be used in order to predict a future brake wear amount for thebrake assembly 200 after a second plurality of predicted future usecycles of the aircraft 100. The second plurality of predicted future usecycles may be a number of cycles after which a brake wear threshold isreached. Each predicted future use cycle may include a respectiveplurality of braking events. For example, the method 1000 may beperformed for each braking event in the second plurality of predictedfuture use cycles. The wear amount from each of those braking events maybe added up to predict the future brake wear amount for the secondplurality of predicted future use cycles. For each predicted future usecycle, the predictions may be based on predicted amounts of energyabsorbed by the brake during respective braking events, and respectivepredicted density parameters of the brake for respective braking events.For example, braking events may be identified and energy absorbed bybrake assembly 200 for those braking events determined based on thepredicted temperature profiles. In other examples, predicted amounts ofabsorbed energy may be based on data from previous cycles. If the brakeassembly 200 is new, or enough previous data is not available, thepredicted amounts of energy may be predetermined.

For the purpose of predicting the future brake wear amount, the method1000 may be used in combination with the method 600 or 700. In theseexamples, the up to date initial thermal oxidation state just beforeeach predicted braking event (e.g. a predicted future braking event) isknown. In this way, the mass of the brake assembly 200, and thereforethe density parameter, may be determined using the initial thermaloxidation before the future braking event in question.

As mentioned above, the second plurality of predicted future use cyclesmay be a number of predicted future cycles after which the predictedfuture brake wear amount reaches a brake wear threshold. For example,the prediction of the future brake wear amount may stop after a cycle inwhich the brake wear threshold is reached. In some examples, theprediction of the future brake wear amount may stop as soon as the totalbrake wear amount reaches the brake wear threshold. The brake wearthreshold may be a total amount of brake wear at which servicing orreplacement of the brake assembly 200 or a component of the brakeassembly 200 is required. For example, a brake assembly such as thebrake assembly 200 of FIG. 2 may require a service if its length L hasbeen reduced by, say, 22% to 24%, depending, for example, on the kind ofdiscs and original, manufactured density thereof. For an exemplary diskhaving an original length L of around 221 mm, a reduction in length ofaround 50 mm may trigger servicing or replacement. In this example, thesecond plurality of predicted future use cycles is the number of cyclesit takes for the total brake wear amount to reach or exceed, forinstance 50 mm (again, for an original disc having a length L of around221 mm).

On the other hand, in some examples, the prediction of the future brakewear amount may stop at the end of a predicted future use cycle duringwhich the total brake wear amount approaches close to the brake wearthreshold such that the total brake wear amount can be expected to reachthe brake wear threshold during the next predicted future use cycle. Insuch examples, the brake wear threshold may be considered reached withinthe second plurality of predicted future use cycles. This is because, inreality, an aircraft 100 with the brake assembly 200 expected to reachthe brake wear threshold in a strict sense in the very next cycle wouldnot be permitted to fly and a service or replacement relating to thebrake assembly 200 may take place at that point.

Using the second plurality of predicted future use cycles, an indicationmay be given as to how many use cycles can take place before the brakeassembly 200 or a component of the brake assembly 200 requires servicingor replacement due to brake wear. In the examples where the brake wearthreshold is strictly reached or exceeded during the last of the secondplurality of future cycles, the number of cycles before a service orreplacement is required due to brake wear may be predicted as one lessthan the number of cycles in the second plurality. In examples where theprediction of the future brake wear amount stops when the brake wearthreshold is expected to be reached in the next cycle after the secondplurality, the second plurality is taken as the number of cycles beforea service or replacement due to brake wear is required.

FIG. 11 is a flow diagram of a method 1100 for determining a number ofgood future use cycles until one of the thermal oxidation threshold andthe brake wear threshold is reached. The number of good future usecycles is the remaining number of future use cycles before one of thethermal oxidation threshold or the brake wear threshold is reached. Themethod 1100 may be performed for a number of predicted future use cyclesuntil the first of the thresholds is reached. The method 1100 involvespredicting a future thermal oxidation state and a future brake wearamount after a predicted future use cycle and, if one of the thermaloxidation threshold and the brake wear threshold is reached, determininga number of good future use cycles before either of the thresholds isreached. If one of the thresholds is not reached, the predictions areperformed for the next predicted future use cycle. As in the aboveexamples, each predicted future use cycle includes a plurality ofbraking event. For each predicted future use cycle the predictions arebased on a respective predicted temperature profile of the brake, acurrent thermal oxidation state, predicted amounts of energy absorbed bythe brake during respective braking events, and respective predicteddensity parameters of the brake for respective braking events.

The number of good future use cycles is a number of cycles after whichservicing or replacement of the brake assembly 200 or a component of thebrake assembly 200 is required. It will be appreciated that service orreplacement in relation to the brake assembly 200 may be carried outwhen one of the thermal oxidation threshold or the brake wear thresholdis first reached. Which threshold is reached first may, for example,depend on the way the aircraft 100 is handled during use and its flightschedule. For example, if the aircraft 100's schedule involves flying tomostly airports with long runways, short taxiing routes, etc., the brakewear threshold may be reached first. This is because, in such examples,the temperature of the brake assembly 200 may not often exceed any ofthe temperature thresholds relating to thermal oxidation. On the otherhand, the aircraft 100 may often experience high energy braking (e.g.due to short runways) causing temperatures above the thresholds relatedto thermal oxidation. In such examples the thermal oxidation thresholdmay be reached first.

At block 1102 of the method 1100, a future thermal oxidation state aftera predicted future use cycle is predicted. The prediction of the futurethermal oxidation state is performed as described above, for example,using an appropriate thermal oxidation model based on a predictedtemperature profile of the predicted future use cycle in question. Atblock 1104 of the method 1100, a future brake wear amount after the samepredicted future use cycle is predicted. The prediction is performed asdescribed above in the context of method 1000.

At block 1106 of the method 1100, it is determined whether the thermaloxidation threshold and/or the brake wear threshold is reached. Forexample, if the thermal oxidation threshold is reached, the method 1100proceeds to block 1108 at which a number of good future use cycles,before either of the thermal oxidation threshold or the brake wearthreshold is reached, is determined, and the method 1100 ends. Forexample, if the thermal oxidation threshold is strictly reached orexceeded after a given number of predicted future use cycles, the numberof good future use cycles is one less than that given number. Forexample, if the thermal oxidation threshold is expected to be reached inthe very next predicted future use cycle, the number of good future usecycles is determined as the number of predicted future use cycles forwhich the method 1100 has been performed thus far.

On the other hand, if it is determined that the brake wear threshold isreached, the method proceeds to block 1108 where a number of good futureuse cycles is determined, and the method 1100 ends. For example, if thebrake wear threshold is strictly reached or exceeded after a givennumber of predicted future use cycles, the number of good future usecycles is one less than that given number. For example, if the brakewear threshold is expected to be reached in the very next predictedfuture use cycle, the number of good future use cycles is determined asthe number of predicted future use cycles for which method 1100 has beenperformed thus far.

If, for example, both the thresholds are reached, the method 1100proceeds to block 1108 where a number of remaining good future usecycles, before either the thermal oxidation threshold or the brake wearthreshold is reached, is determined and the method 1100 ends. In thisexample, if at least one of the thresholds is strictly reached orexceeded after a given number of predicted future use cycles, the numberof good future use cycles is one less than that given number. Otherwise,the number of good future use cycles is determined as the number ofpredicted future use cycles for which the method 1100 has been performedthus far.

If the brake wear threshold is not reached, the method 1100 proceeds toblock 1110 and blocks 1102 to 1110 are repeated for the next predictedfuture use cycle.

In this way, a number of good future use cycles may be predicted basedon which of the thermal oxidation threshold and the brake wear thresholdis reached first. This is because, the brake assembly 200 may require aservice or replacement, or a component of the brake assembly 200 mayrequire a service or replacement once the first of these thresholds isreached. It will be appreciated, for example, that brake assembly 200will not continue to be used if the thermal oxidation threshold isreached but the brake wear threshold is not. It should also beappreciated that blocks of the method 1100 may be performed in anysuitable order. For example block 1104 may be performed before block1102 and/or block 1110 may be performed before block 1106.

One or more of the above described methods, namely the methods 600, 700,1000 and 1100, or any of their variations (e.g. live determination ofoxidation or brake wear, or prediction of future thermal oxidation stateor future brake wear, etc.) may be performed by a processor of thecomputing system 106 of the aircraft 100, for example, based oninstructions stored in a computer readable storage medium of thecomputing system 106. For example, monitoring of the thermal oxidationstate (subsequent to use cycles or live) may be performed by a processorof computing system 106. Alternatively, or in addition, monitoring ofthe brake wear (subsequent to use cycles or live) may be performed by aprocessor of the computing system. Alternatively, or in addition to anyof these examples, predictions relating to the future thermal oxidationstate and/or the future brake wear state may be performed by a processorof the computing system 106. The methods may be performed, for example,using data from the instruments 108. For example, temperature data asmeasured by the temperature sensor 216 may be used. In the case ofprediction, the future temperature profiles and/or other predicted datamay be predicted by a processor of the computing system 106.Alternatively, the data for prediction may be determined on a computingsystem not on board the aircraft 100, and may be stored in a computerreadable storage medium of the computing system 106.

In the foregoing examples, the apparatus 300 is described as beinginstalled on a vehicle such as the aircraft 100. The apparatus 300 maybe comprised in the computing system 106 of the aircraft 100. Forexample, the first controller 302 may be implemented by a processor ofthe computing system 106. Said processor may implement instructionstored on a computer readable storage medium of the computing system 106to implement the functions of the first controller 302. The brakingsystem 214 may be implemented by the computing system 106 in a similarmanner. Alternatively, the apparatus 300 and/or the braking system 214may be implemented by items of apparatus separate to the computingsystem 106. For example, there may be dedicated processors to implementthe functions of the first controller 302 and/or the second controller304 provided on the aircraft 100. In some examples, the foregoingdescribed functions and processes of the apparatus 300 may be performedby the braking system 214. In some examples, the first controller 302and the second controller 304 may be implemented by the same processoror the same group of processors. In some examples, the first controller302 and the second controller 304 may be implemented by differentprocessors or different groups of processors.

All or part of the instructions for performing the aforementionedprocesses may be generated and/or the processes may be performed usingany suitable software or combination of software. In one example,“MATLAB” and/or “SCADE” may be used to generate all or part of theinstructions for respective processors to carry out any of theaforementioned processes. In other examples, other software packages maybe used. For example, any suitable programming language, developmentenvironment, software package, or the like may be used. Other examplesof programming languages include PYTHON, C++, C, JAVASCRIPT, FORTRANetc.

It is to noted that the term “or” as used herein is to be interpreted tomean “and/or”, unless expressly stated otherwise. Although the inventionhas been described herein with reference to one or more preferredexamples, it will be appreciated that various changes or modificationsmay be made without departing from the scope of the invention as definedin the appended claims.

1. An apparatus comprising: a controller configured to: generate a firstindication for a vehicle braking system depending upon an oxidationstate of a wheel brake of the vehicle.
 2. The apparatus according toclaim 1, wherein: the controller is configured to: determine a braketemperature characteristic criterion of the brake according to theoxidation state of the brake; determine whether a temperaturecharacteristic of the brake satisfies the brake temperaturecharacteristic criterion; and generate the first indication for thebraking system depending upon whether the brake temperaturecharacteristic satisfies the brake temperature characteristic criterion.3. The apparatus according to claim 2, wherein the controller receivesan indication of the temperature characteristic of the brake from atemperature sensor associated with the brake.
 4. The apparatus accordingto claim 2, wherein the controller receives a predicted temperaturecharacteristic from a brake temperature prediction function as thetemperature characteristic of the brake.
 5. The apparatus according toclaim 2, wherein the controller is configured to: monitor thetemperature characteristic of the brake; and if the temperaturecharacteristic of the brake no longer satisfies the brake temperaturecharacteristic criterion, generate a second indication for the brakingsystem that the temperature characteristic of the brake no longersatisfies the brake temperature characteristic criterion.
 6. Theapparatus according to claim 2, wherein: the temperature characteristicof the brake comprises a temperature of the brake; and the braketemperature characteristic criterion is satisfied if the temperature ofthe brake exceeds a brake temperature threshold.
 7. The apparatusaccording to claim 6, wherein the controller is configured such that thehigher the level of thermal oxidation of the brake, the lower the braketemperature threshold of the determined brake temperature characteristiccriterion is.
 8. The apparatus according to claim 7, wherein, if thethermal oxidation state of the brake is below a predetermined thermaloxidation level, a first brake temperature characteristic criterion isselected which comprises a first temperature threshold.
 9. The apparatusaccording to claim 8, wherein, if the thermal oxidation state of thebrake is above the predetermined thermal oxidation level, a second braketemperature characteristic criterion is selected which comprises asecond temperature threshold lower than the first temperature threshold.10. The apparatus according to claim 9, wherein the second braketemperature characteristic criterion is selected based on the differencebetween the thermal oxidation state of the brake and the predeterminedthermal oxidation level.
 11. A braking system of a vehicle comprising: acontroller configured to: receive a first indication, the firstindication having been generated depending upon an oxidation state of awheel brake of a vehicle; and control the operation of the brake basedon the first indication.
 12. The braking system according to claim 11,wherein: the first indication received by the controller is generateddepending upon whether a brake temperature characteristic satisfies abrake temperature characteristic criterion; and the controller isconfigured to: receive a second indication that the temperaturecharacteristic of the brake no longer satisfies the brake temperaturecharacteristic criterion; and control the brake selectively to beenabled or disabled based on the received indication.
 13. The brakingsystem according to claim 11, wherein the controller is configured tocontrol the brake to be disabled if it receives the first indication.14. The braking system according to claim 13, wherein the controller isconfigured to control the brake to be enabled if it receives the secondindication.
 15. The braking system according to claim 13, wherein thevehicle is an aircraft and the controller is configured to disable abrake if a taxiing criterion is met, wherein the taxiing criterioncomprises one or more of: an aircraft speed threshold defined such thatan aircraft speed less than or equal to the aircraft speed thresholdsatisfies the predefined taxiing criterion; and a particular flightphase indicated by a flight phase indication system of the aircraft. 16.The braking system according to claim 13, wherein the controller isconfigured to: receive a braking request, the braking request comprisinginformation relating to a requested braking intensity; determine, basedon the information related to the requested braking intensity, whetherthe requested braking intensity exceeds a braking intensity threshold;and if the requested braking intensity exceeds the braking intensitythreshold, enable at least one disabled brake.
 17. A method forcontrolling at least one wheel brake of an aircraft, the methodcomprising: generating a first indication depending upon an oxidationstate of a wheel brake of an aircraft; and controlling the brake to bedisabled based on the first indication.
 18. The method according toclaim 17, comprising: determining a brake temperature characteristiccriterion of the brake according to the thermal oxidation state of thebrake; determining whether a temperature characteristic of the brakesatisfies the brake temperature characteristic criterion; and generatingthe first indication depending upon whether the brake temperaturecharacteristic satisfies the brake temperature characteristic criterion.19. The method according to claim 18, comprising: (i) monitoring thetemperature characteristic of the brake; (ii) determining whether thetemperature characteristic of the brake still satisfies the braketemperature characteristic criterion; if the temperature characteristicof the brake no longer satisfies the brake temperature characteristiccriterion: generating a second indication that the temperaturecharacteristic of the brake no longer satisfies the brake temperaturecharacteristic criterion; and controlling the brake to be enabled basedon the second indication; and if the temperature characteristic of thebrake still satisfies the brake temperature characteristic criterion,repeating (i) and (ii).
 20. The method according to claim 18 comprisingreceiving an indication of the temperature characteristic of the brakefrom a temperature sensor associated with the brake.
 21. The methodaccording to claim 18 comprising receiving a predicted temperaturecharacteristic from a brake temperature prediction function as thetemperature characteristic of the brake.
 22. The method according toclaim 18, wherein: the temperature characteristic of the brake comprisesa temperature of the brake; and the brake temperature characteristiccriterion is satisfied if the temperature of the brake exceeds a braketemperature threshold.
 23. The method according to claim 22, wherein thehigher the level of thermal oxidation of the brake, the lower the braketemperature threshold of the determined brake temperature characteristiccriterion is.
 24. The method according to claim 23, wherein, if thethermal oxidation state of the brake is below a predetermined thermaloxidation level, a first brake temperature characteristic criterion isselected which comprises a first temperature threshold.
 25. The methodaccording to claim 24, wherein, if the thermal oxidation state of thebrake is above the predetermined thermal oxidation level, a second braketemperature characteristic criterion is selected which comprises asecond temperature threshold lower than the first temperature threshold.26. The method according to claim 25, wherein the second braketemperature characteristic criterion is selected based on the differencebetween the thermal oxidation state of the brake and the predeterminedthermal oxidation level.
 27. The method according to claim 17, whereinthe wheel brake is disabled if a predefined taxiing criterion is met,wherein the predefined taxiing criterion comprises one or more of: anaircraft speed threshold defined such that an aircraft speed less thanor equal to the aircraft speed threshold satisfies the predefinedtaxiing criterion; and a particular flight phase indicated by a flightphase indication system of the aircraft.
 28. The method according toclaim 17, wherein the method comprises: receiving a braking request, thebraking request comprising information relating to a requested brakingintensity; determining, based on the information related to therequested braking intensity, whether the requested braking intensityexceeds a braking intensity threshold; and if the requested brakingintensity exceeds the braking intensity threshold, enabling at least onedisabled brake.